在MATLAB中繪製橢圓對象的主軸和副軸

該程序當前輸入硬幣的圖像，對其進行閾值處理，對其進行二值化處理，並使用regionprops函數查找分段橢圓的長軸和短軸長度。我如何輸出一個繪製用於計算原始圖像上的'MajorAxisLength'和'MinorAxisLength'軸的子圖？在MATLAB中繪製橢圓對象的主軸和副軸

我附上了我的代碼，供您細讀。

% Read in the image. 
folder = 'C:\Documents and Settings\user\My Documents\MATLAB\Work'; 
baseFileName = 'coin2.jpg'; 
fullFileName = fullfile(folder, baseFileName); 
fullFileName = fullfile(folder, baseFileName); 
if ~exist(fullFileName, 'file') 
    fullFileName = baseFileName; % No path this time. 
    if ~exist(fullFileName, 'file') 
     %Alert user. 
     errorMessage = sprintf('Error: %s does not exist.', fullFileName); 
     uiwait(warndlg(errorMessage)); 
     return; 
    end 
end 

rgbImage = imread(fullFileName); 
% Get the dimensions of the image. numberOfColorBands should be = 3. 
[rows columns numberOfColorBands] = size(rgbImage); 
% Display the original color image. 
subplot(2, 3, 1); 
imshow(rgbImage, []); 
title('Original color Image', 'FontSize', fontSize); 
% Enlarge figure to full screen. 
set(gcf, 'Position', get(0,'Screensize')); 

% Extract the individual red color channel. 
redChannel = rgbImage(:, :, 1); 
% Display the red channel image. 
subplot(2, 3, 2); 
imshow(redChannel, []); 
title('Red Channel Image', 'FontSize', fontSize); 
% Binarize it 
binaryImage = redChannel < 100; 
% Display the image. 
subplot(2, 3, 3); 
imshow(binaryImage, []); 
title('Thresholded Image', 'FontSize', fontSize); 

binaryImage = imfill(binaryImage, 'holes'); 
labeledImage = bwlabel(binaryImage); 

area_measurements = regionprops(labeledImage,'Area'); 
allAreas = [area_measurements.Area]; 
biggestBlobIndex = find(allAreas == max(allAreas)); 
keeperBlobsImage = ismember(labeledImage, biggestBlobIndex); 
measurements = regionprops(keeperBlobsImage,'MajorAxisLength','MinorAxisLength') 

% Display the original color image with outline. 
subplot(2, 3, 4); 
imshow(rgbImage); 
hold on; 
title('Original Color Image with Outline', 'FontSize',fontSize); 
boundaries = bwboundaries(keeperBlobsImage); 
blobBoundary = boundaries{1}; 
plot(blobBoundary(:,2), blobBoundary(:,1), 'g-', 'LineWidth', 1); 
hold off;

來源

2012-04-02 mg6011

我和你2年前做過的一些項目有同樣的任務。我已經修改了我在下面爲您使用的代碼。它涉及計算數據點的協方差矩陣並找出它們的特徵值/特徵向量。這裏請注意，由於圓對稱，小軸和長軸會有些「隨機」。另外請注意，我以非常幼稚的方式製作了圖像二進制文件，以便簡化代碼。

% Load data and make bw 
clear all;close all; clc; 
set(0,'Defaultfigurewindowstyle','docked') 

I = imread('american_eagle_gold_coin.jpg'); 
Ibw = im2bw(I,0.95); 
Ibw = not(Ibw); 

figure(1);clf 
imagesc(Ibw);colormap(gray) 

%% Calculate axis and draw 

[M N] = size(Ibw); 
[X Y] = meshgrid(1:N,1:M); 

%Mass and mass center 
m = sum(sum(Ibw)); 
x0 = sum(sum(Ibw.*X))/m; 
y0 = sum(sum(Ibw.*Y))/m; 

%Covariance matrix elements 
Mxx = sum(sum((X-x0).^2.*Ibw))/m; 
Myy = sum(sum((Y-y0).^2.*Ibw))/m; 
Mxy = sum(sum((Y-y0).*(X-x0).*Ibw))/m; 

MM = [Mxx Mxy; Mxy Myy]; 

[U S V] = svd(MM); 

W = V(:,1)/sign(V(1,1)); %Extremal directions (normalized to have first coordinate positive) 
H = V(:,2); 
W = 2*sqrt(S(1,1))*W; %Scaling of extremal directions to give ellipsis half axis 
H = 2*sqrt(S(2,2))*H; 

figure(1) 
hold on 
    plot(x0,y0,'r*'); 
    quiver(x0,y0,W(1),H(1),'r') 
    quiver(x0,y0,W(2),H(2),'r') 
hold off

Original image Axis found from binary image enter image description here